LAUSR

Abstract Haemaphysalis longicornis Neumann is a widely distributed species known for its capacity to transmit pathogens of medical, public health, and veterinary importance. Due to the environmental contamination caused by synthetic acaricides, plant essential oils have emerged as a promising alternative to manage tick infestation. This study evaluated the ultrastructural and morphological changes induced by Cymbopogon citratus Stapf (lemongrass) essential oil on adult H. longicornis tick. The concentrations of lemongrass essential oil used for the treatment via the adult immersion test were from 10 to 40 mg/mL. The most significant alterations 24 h post-exposure include the proliferation of lysosomes, reduction in the number of the rough endoplasmic reticulum, disorganization of the microvilli, the disappearance of lipid droplets and hematin granules, and cytoplasmic vacuolization (midgut); a thinner endocuticle and epicuticle, the deletion of the subdivision's demarcation of the procuticle, disfiguration of the lamellar arrangements of the exocuticle, and cytoplasmic vacuolization of the epithelial cells (integument); cracks on the sensilla sockets, the detachment of one or two sensilla in the anterior pit, and partial disfiguration of part of the slit's edge (Haller's organ). These results reflect the acaricidal properties of the essential oil and could be an alternative means of tick control.